1. Field of the Invention
This invention relates to suction cleaning heads of the kind having a suction chamber which has an internal liquid distributor for connection to a source of cleaning liquid and which is adapted to deliver the cleaning liquid to a surface to be cleaned. Examples of cleaning heads of this kind are disclosed in British patent specifications 1291138, 1121225 and 1601455.
2. BACKGROUND OF THE RELATED ART
The cleaning head disclosed in specifications 1291138 and 1121225 has an internal liquid distributor in the form of a cross-tube which is provided with a plurality of downwardly depending fingers which incorporate fluid passageways for delivering cleaning liquid to the surface to be cleaned. The liquid is caused to flow into the internal cross-tube from the source of cleaning liquid and from the downwardly depending fingers as a result of the influence of low pressure created at the mouth of the suction chamber when the mouth is in engagement with the surface to be cleaned.
When the mouth is out of engagement with the surface, the required low pressure conditions do not exist in the vicinity of the outlets of the fluid passageways and therefore liquid should not be drawn from the fingers in the absence of such low pressure. Accordingly, delivery of cleaning liquid to the surface when the cleaning head is initially applied thereto will be delayed until the liquid has been drawn from the source to the suction head.
However, in circumstances where the suction head is located lower than the source, once the liquid has been delivered to the suction head fluid flow will be maintained as a result of syphonic action even when the suction head is not applied to a surface, and this can result in an uncontrolled flow of cleaning liquid from the head. This uncontrolled flow needs to be controlled by utilisation of a separate valve which will close off the delivery line whereby the cleaning liquid is supplied to the suction head, when the latter is not in contact with the surface. Therefore, while the flow of cleaning liquid to the cleaning head is initiated as a result of the influence of low pressure generated at the cleaning head when applied to the surface to be cleaned, the continuance of such flow is not so controlled.
An additional difficulty which is caused by the cleaning heads as disclosed in specifications 1291138 and 1121225 resides in the fact that the liquid is injected into the carpet by utilisation of a plurality of downwardly depending fingers which can project below the plane of the open mouth of the suction head and will engage the carpet fibres where the surface to be cleaned comprises a carpet. As a result, the suction head can become very difficult to move across the carpet and such movement can cause damage to the carpet fibres, particularly in the case of loop pile carpets.
A further difficulty with suction device resides in the limitation of the width of the cleaning which can be used in accordance with that design. The flow of liquid to the cleaning head is the result of low pressure which is induced in the suction head when applied to floor surface, and due to the limited nature of such flow, the width of the cleaning head is determined by the rate of which the cleaning liquid can be delivered thereto. If the cleaning head is of too great a width, the cleaning liquid drawn to the suction head will be applied through the central fingers only.
A still further difficulty with these cleaning heads is that the cleaning liquid is drawn away immediately on discharge from the apertures in the fingers before the cleaning liquid has time to thoroughly penetrate the carpet fibres and dissolve any soil or dirt therein. Such rapid removal results in inadequate cleaning and the use of excessive volumes of cleaning liquid.
The cleaning head disclosed in British specification 1601455 has an inner compartment containing a small transverse duct through which cleaning liquid is delivered by the influence of some external means such as gravity or a pressurised supply to fine outlets at a position spaced inwardly from the mouth of the cleaning head and shielded from the air flow within the suction head by the side walls of the inner compartment. Whilst this obviates many of the above mentioned difficulties, the cleaning liquid is still delivered to the cleaning head by a means which is independent of the function of the cleaning head and which requires an overriding control through a shut-off valve or the like. As a result, in the event that the cleaning head is inadvertently left with the shut-off valve open after a period of use, the cleaning liquid may continue to be delivered to the cleaning head by syphoning action.